TABLE 1 Summary of Three Demographic Types High Birth High Birth Low Birth High Death Low Death Low Death (Mainly in (Mainly in Tropical Europe, Northern Africa, Parts of (Mainly in Asia, America, Oceania, Asia) Latin America) U.S.S.R., Japan) (1) U) (3) Number about 1970 (billions) 0.5 2.0 1.0 Percent increase/year 2 3 0.7 Time to double (years) 35 23 100 Doublings per century 3 4 1 Number in year 2070 if present rates continue (billions) 4 32 2 Source: Author's calculations. energy for fuel oil. It increases crop output per unit of land input as well as per unit of labor. But the rising income that goes with improving technology demands more space. It substitutes beef for bread-which is at least a fivefold extension of the land base needed per person; it builds freeways rather than footpaths; it contaminates the air and water. Whether on balance the high-technology-high-income combination has a greater carrying capacity than traditional peasant exploitation of a given area is uncertain, but even if it has, the increase of 0.7 percent per year cannot continue very long. The same is true, with greater certainty, for the other two groups. We can suppose that the death rate for tropical Africa will go down and that a further decline in the death rate for the less developed world as a whole is in prospect. The few and small countries for which we have registrations over a series of years provide a suggestion of this trend. Mauritius had a crude death rate of 12.86 per 1,000 in 1955, 8.83 by 1966. The Mauritian expectation of life had gone up 6 years for males and 7 years for females during the same period of 11 years. Jamaica rose by 7 and 9 years for males and females respectively from 1951 to 1963; Mexico by 4 years for both males and females from 1960 to 1966. Other countries rose less, but advances in the expectation of life at age 0 of 5 years per decade are typical for the less developed world. Declines in birth rates appear conspicuously in some of the countries around the rim of Asia: Taiwan fell from a crude rate of 44.20 per 1,000 in 1956 to 31.88 in 1966; Hong Kong from 34.40 in 1961 to 25.84 in 1966; Ceylon from 39.35 in 1953 to 31.56 in 1967; Singapore from 43.22 in 1957sequences for the world's future population if the present rates continue. The first conclusion is that they cannot continue for a century; if they did, the world would contain 38 billion people.